Furnace control



Dec. 29, 1936.

L. R] KETTENRING ET AL FURNACE CONTROL 3 Sheets-Sheet 1 Filed Nov. 6, 1934 Louis R. Ketteming Francis J. Lillis Dec. 29, 1936. R. KETTENRING ET AL 2,065,712

FURNACE CONTROL Filed Nov. 6, 1954 3 Sheets-Sheet 2 lJ lI Louis R. Ketteming VohAme '..c..)

Dec. 29,- 1936.

L. R. KETTENRING ET AL FURNACE CONTROL Filed Nov. 6, 1934 3 Sheets-Sheet 3 1401 115 R. Kzlaen'rind Francis J.L'111i 33., gm A W CTI Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE FURNACE CONTROL Application November 6, 1934, Serial No. 751,726

7 Claims.

Our invention relates to furnaces or like heating plants, particularly to such furnaces which employ a circulating medium, such as hot air or hot water, which is heated by the furnace, flows outward to registers or to heat exchange devices in the rooms to be heated, and then is returned to the furnace to be reheated. While our invention is particularly designed for employment in conjunction with hand-fired furnaces, it is also con templated that the same may be employed in conjunction with stokers, hopper-fed burners, or indeed with any type of burner wherein there is employed a substantially continuous fire.

The automatic regulation of oil burners has proven so satisfactory that in districts where oil can be obtained cheaply it has largely supplanted coal-burning devices, even though it may be possible to produce coal economically in such regions. This is true largely because of the ease of control and the possibility of regulation of temperature with oil burners within close limits, and because there has not been available heretofore, so far as we are aware, an automatic regulator for coalburning furnaces which will maintain a constant temperature within the same limits as temperatures can be maintained through the use of oil burners. It is undesirable, wasteful, and unhealthful to fire a coal furnace in the manner usually deemed necessary, namely, by firing heavily when a fresh charge of coal is supplied, then banking the fire until the temperature has been reduced below the point of comfort, and then forcing the fire again. It is a prime object of our invention, therefore, to provide means and a method of regulating such furnaces burning coal and like substances, whereby the temperature of the circulating medium, and therefore of the house being heated, may be maintained substantially constant within close limits, even closer than with an oil burner as usually controlled, thereby entailing the further advantages of economy in fuel, less difficulty in handling and cleaning the furnaces, and greater conservation of health of persons within the building.

Thermostatic devices have been proposed heretofore for the operation of draft-controlling devices of a furnace, but these have usually been either of the. type requiring the employment of a relay to set in operation a more powerful force than can be exerted by the thermostat itself, or if it has been attempted to connect the thermostat directly to the draft controlling devices, the thermostat must be made very heavy in order to effect proper operation, and therefore is not sufncie'ntl'y responsive to slight temperature changes.

Furthermore, any bimetal thermostat, particularly one which is strong enough to operate a draft door and check damper directly, is not sensitive to small changes within a low range of temperature; it is only responsive to small changes at higher temperatures. In consequences, any such thermostat, directly connected to draft-controlling devices, must be so placed as to be heated by the higher temperatures obtaining within the furnace casingfor instance, above the furnace body, or in a location where it is shielded from the cooling effect of the returning cold air. Thus located it may respond to changes in temperature in the furnace itself, but not to the changes in temperature of the returning air, which is the true index of the temperature of the house. It is therefore a further object to provide thermally responsive means directly and mechanically connected to draft-controlling devices which will i have sufficient power to operate them, and yet will be so located as to be quickly responsive to slight temperature changes in the house being heated, and particularly to temperature changes within a given low range.

It is a further object to provide an arrangement of a draft-controlling device with a direct connected mechanical device to operate the same, and a thermally responsive device, usually distant from the operating device, but directly connected to the same, so that the thermally responsive device may be placed in that part of the circulating system wherein it operates between the limits of its most effective range, and'where it most accurately corresponds to the temperature of the house.

Other objects will appear as this specification progresses.

Hereafter we shall disclose how two draft-controlling devices may be employed, the one a draft door and the other a check damper, and the term draft-controlling device as hereinafter used shall be understood to mean either or both of these devices, or any equivalent device, unless the context requires otherwise.

Our invention comprises the novel combination as a whole, the novel combination of parts constituting a thermally responsive operating device, and the novel method of controlling a furnace, all as shown in the accompanying drawings, described in this specification, and defined by the claims terminating the same.

In the accompanying drawings We have shown our device incorporated in different types of furnaces, and in various modified forms.

Figure 1 is a part elevation and part section of a hot air furnace, with our device incorporated therein.

Figure 2 is an elevation of the control device, with parts broken away.

Figure 3 is a similar View of a modified form of the device, particularly designed for stoker operation.

Figure l is a part section and part elevation of a hot water furnace, illustrating the manner in which our device may be incorporated therein.

Figure 5 is a temperature-volume curve, showing the most effective range of the fluid with which the system is filled.

Figure 1 shows the device incorporated in a hot air furnace, which is the most commonly used domestic installation, this comprising a furnace body 9 having a draft door 8 leading to the ash pit space beneath the grate 90, and having the smoke pipe 9| with a check damper 80. The furnace body is surrounded with the usual casing 92, into the bottom of which leads the cold air return or boot 93, and from the top of the casing extend the hot air conduits 94. Such a furnace may be fired by fuel supplied through the fire door 95. Such a furnace is usually manually controllable from a room above by means of a tension device such as the cable or chain I, connected to the draft door 8 and extending upward to a manual operator such as the catch device ID in the room above, with which the chain may be engaged to hold the draft door open, and from which it may be disengaged to drop the draft door closed. Such a manual control may be employed in conjunction with our automatic control, so that the fire may be banked at night or may be temporarily forced. Similarly the check damper is frequently controlled by such a manual device, though the same has been omitted from the drawings for clearer illustration, and this manual check damper control may still be employed, if desired.

, Our automatic control may be connected to such a typical system without substantial modification thereof. A thermally responsive device, such as the tubular chamber I, is supported by suitable means, as for example the curved pipe I0 and collar II, within the casing 92, and is preferably located in the vicinity of the cold air return to the casing, in a region where it will not be. affected by the highest temperatures communicated to the circulating medium, but rather in a region where it will be affected chiefly by changes in temperature of the returning medium. Usually this is at the back or side of the furnace, not in front.

At the front of the furnace, or in a position where it can conveniently be mechanically connected to the draft door or engaged with the pull chain 1 connected therewith, we mount our control device, which incorporates a pressure responsive device, such as the sylphon bellows 2, which is a closed expansible and compressible chamber. Connecting the thermally responsive device I and the bellows 2 is a conduit 3 which preferably extends at one end to a point adjacent to the bottom of the chamber within the tube I, and at its other end communicates with the interior of the bellows 2. A spring 4 with a regulating screw 40 bears upon the bellows, opposing any tendency to expand with a yielding force which is governable by the screw 40. The spring may bear directly upon the bellows or upon a block 20 which is secured to or which rests upon the end of the bellows.

An arm 5, fulcrumed at 50 adjacent to the bellows, is engageable with the bellows, whereby the latter controls movement of the arm. This connection may be by means of engagement of the end of the arm 5 within a recess in the block 20, and this connection may be augmented by a pivot pin 5I. The entire device thus described may conveniently be encased within a suitable cabinet, designated by the numeral 22, from which the longer end of the arm 5 projects. Thus the projecting portion of the arm 5 is given a multiplied movement directly under control of the expansion and. contraction of the bellows 2.

Carried near the end of the arm 5 is a guide, such as the pulley 52, about which passes the chain or cable I, and a second fixed guide or pulley I2 is so disposed as to bring a length 13 of the cable or chain in line with the arm 5. As will appear hereafter, this provides a means for automatic regulation of the position of the draft door 8, but it is desirable also to control the check damper 80, and to this end a second chain or cable 8| extends from the check damper 80 over suitable guide pulleys 82 to a connection to the arm 5, and the point of this connection may be variable, as indicated by the several holes 58, in order that proper relative movement may be given to the draft door 8 and the check damper 80.

The thermal system, consisting of the bellows 2, the conduit 3, and the chamber I, is filled with a fluid, and should be filled with such a fluid as gives the greatest degree of expansion and contraction, and therefore the greatest volume change, within a range comparable to the temperature of the return air or other circulating medium, after it hasbeen somewhat heated by entrance into the furnace casing. We have found acetone to be ideal for this purpose, inasmuch as Figure 5 will show that its temperature-volume curve rises steeply from to about F., above which its volume changes but little, since it boils at 134.4 F. Thus its critical range for temperature-volume factors is between 120 and 130 F. By somewhat lessening the pressure imposed upon the acetone, its critical range may be dropped to the neighborhood of 100 F. Located adjacent to the cold air return, it can be maintained, for normal temperatures in the house of the order of 70 F.. at about this critical range of temperature.

It will now be evident that as the house cools off, and therefore the return air cools, the fluid in the chamber I will contact appreciably even for a slight drop in temperature in the vicinity of 130 F., and pressure on the bellows 2 will drop sharply, contracting the bellows and causing the outer end of the arm 5 to rise. If the chain or cable I is fixed at the point I0, raising the arm 5 will raise the draft door 8, and this will supply additional air for combustion, resulting in the production of more heat and a higher temperature. The cables I and 8| are at this time arranged so that the check damper 80 is closed. Now as the house heats up, the return air is more highly heated, and this causes expansion of the acetone and causes the outer end of the arm 5 to drop. The first effect will be to close the draft door, but if the rise in temperature continues, the check damper 80 will eventually be raised, and either of these results or their combination will effect checking of the fire and the consequent decrease in temperature. In actual practice the check damper usually remains closed and the draft door is slightly open, maintaining a. continuous fire and a control which is very sensitive within two or three degrees in the house. A further advantage of this continuous slow firing is to prevent clinkering in the coal. The cheapest grades of coal may be made to burn continuously to a fine powder, whereas with alternate heavy firing and banking, clinkers are formed.

If it is desired to bank the fire for the night, it is only necessary to drop the chain or cable 1 through control at the point 10, and this so increases the effective length of the chain or cable that raising of the arm 5 to its extreme limit will not raise the draft door 8. As has been previously noted, a manual control may also be employed to raise the check damper, when it is desired to bank the fire.

Such a system may be incorporated in a hot water furnace, such as that shown in Figure 4 in a more or less diagrammatic fashion, and in such a system the thermally responsive device I may be inserted within the return pipe 96 of the hot water system. The connection to the draft door and to any check damper may be the same as that illustrated in Figure l and has been omitted from Figure 4.

Stokers are generally controlled through the operation of a motor which drives a feed screw or like device, and which also drives a fan or blower, which in this instance would constitute a draftcontrolling device. To control such a stoker. therefore, it is only necessary to control the motor, and an arrangement to this end is shown in Figure 3. A control device, such as a common mercury switch or contactor, is illustrated at 6, mounted upon a lever 60 pivoted at 6|. The spaced contacts 62 are connected electrically to terminals 63 in the motor circuit, or in a control circuit for such a motor. Tilting of the lever 60, and therefore of the contactor 6, is effected by means of a link 64 connected to one arm of the lever 60, and having a slot 65 engageable by a pin 65, carried by the arm 5.

The terminals 63 may form part of an alarm circuit, to warn an attendant that the furnace is firing strongly, usually indicating that the supply of fuel islow. If so used, it is only necessary to give warning until the temperature begins to rise, whereupon the warning circuit may be opened. T0 effect this a spring 6! may be employed, which will permit the arm 5 to drop, but will shortly thereafter effect movement of the lever 60 to open the circuit. This spring would be omitted if the device is used as a stoker control, tilting of the lever 60 being effected as previously described.

As the acetone or other fluid in the thermal system contracts, the outer end of the arm 5 rises, and the pin 66, engaging the upper end of the slot 65, tilts the lever 60 until the mercury runs to the end of the contactor 6, wherein are secured the contact points 62, and this constitutes a quick throw device, or if desired, any suitable additional quick throw or snap-over device may be employed in conjunction with the contactor. The circuit being closed, the stoker motor is energized, more fuel is fed to the fire, and the blower begins to supply more air. As the temperature in the circulating system increases and the acetone expands, the outer end of the arm 5 drops until the pin 66 engaging the lower end of the slot 65 tilts the lever 60 back until the contactor is thrown to the opposite position, throwing the contact points 52 out of the circuit and stopping the motor.

While this latter device has been described particularly in conjunction with the ordinary coal stoker, it will be evident that it may be employed in conjunction with any device of a similar nature, and might indeed be employed in conjunc-. tion with an oil burner, but we prefer that our system be employed in conjunction with burners wherein a more or less steady or continuous fire is maintained within the furnace.

While it may not be possible to locate the member I so exactly that it will maintain initially the desired temperature in the circulating system, nevertheless it may be so located that it controls within the range of temperatures indicated by the curve of Figure 5, and any discrepancy may be compensated for by'the adjusting screw 40. varying the force applied by the spring 4.

It is desired to point out that the vapor pressure generated in such a system exerts a very considerable force, and that this force is directly applied to the draft-controlling device or devices to move them, consequently no relay device is necessary, and much more exact and reliable control may be effected by such means as that we have described.

What we claim as our invention is:

1. In combination with the draft door of a furnace, a tension member connected thereto to open or close it, manual means above the draft door to fix said tension member in position to hold the door open or to permit it to close, an arm fulcrumed above the draft door, guide means carried by said arm and engageable with said tension member, fixed guide means directing the line in line with said arm and thence upward to said manual means, and means operatively engaged with said arm and responsive to thermal changes in the return fiow to the furnace of a heated circulation medium to raise said arm upon decrease in temperature of the medium, thereby tending to open the draft door, and to lower said arm upon increase in such temperature, thereby tending to close the draft door.

2. The combination of claim 1, wherein the last-mentioned means consists of a thermally responsive member adapted to be disposed in the return flow, a sylphon bellows directly engaged with the arm, a conduit connecting the two, and a fluid filling the bellows conduit, and thermally responsive member, and expansible with increase of temperature in the latter member.

3. In combination with the arrangement defined in claim 1, a check damper for the furnace, and a mechanical connection from the arm to said check damper, arranged to close the check damper by movement of the arm upward, and to open the check damper by downward movement of the arm.

4. In combination with a furnace having a furnace body surrounded by a casing defining an air chamber communicating with a hot air conduit in the top thereof, and a return conduit in the bottom thereof for intake thereinto of relatively cooler air, and with fire controlling means associated with the furnace, means to actuate said fire controlling means, thermally responsive means containing a fluid having a temperaturevolume curve which rises steeply between about and F., and which is relatively flat at temperatures above and below such range, said thermally responsive means being disposed entirely within said air chamber above said cold air return conduit but below the top of said furnace body and spaced from the wall thereof, and at a point at which the air temperature normally lies within such temperature range of 100 to 130 F., and fluid-filled operating means to move the fire control actuating means, in response to changes in said thermally responsive means under the influence of temperature changes in said air chamher.

5. The combination of claim 4, wherein the fluid contained in the thermally responsive means is acetone, partly in the vapor state and partly in the liquid state.

6. In combination with a furnace having a circulating system for a heated medium, and with fire controlling means associated with said furnace, a member directly connected to said fire controlling means, a pressure chamber, expansible under increased pressure and contractable under decreased pressure, engaging said member to move the same, a closed chamber adapted for insertion within the circulating system, a conduit connected to said pressure chamber and projecting downward through said closed chamber to a point near the bottom thereof, and a liquid filling completely said pressure chamber and said conduit, and nearly filling said closed chamber, said liquid being readily vaporizable or condensable upon an increase or decrease, respectively, in the temperature of said closed chamber, to increase or decrease, respectively, the pressure of the vapor upon the surface of the liquid in the closed chamber, thereby eifecting a corresponding change in liquid pressure in said closed chamber, conduit and pressure chamber, to move the member connected to said fire controlling means.

7. The combination of claim 6, wherein the easily vaporizable liquid employed is acetone.

LOUIS R. KETIENRING. FRANCIS J. LILLIS. 

